Programmable controller, called Programmable Controller in English, referred to as PC. However, since PCs are easily confused with personal computers, people are still accustomed to using PLCs as abbreviations for programmable controllers. It is a microprocessor-based digital computing operation electronic system device designed for industrial field applications. It uses programmable memory to perform logic operations, sequence control, timing/in its internal memory. Operational instructions such as counting and arithmetic operations, and control various types of mechanical or production processes through digital or analog input and output interfaces. PLC is a combination of microcomputer technology and traditional relay contact control technology. It overcomes the shortcomings of complicated wiring, low reliability, high power consumption, versatility and poor flexibility of mechanical contacts in relay contact control systems. Make full use of the advantages of the microprocessor, and take care of the skills and habits of the on-site electrical operation and maintenance personnel, especially the programming of the PLC, without the need for specialized computer programming language knowledge, but based on a relay ladder diagram The simple instruction form makes the user program image, intuitive, convenient and easy to learn; debugging and error checking are also very convenient. After purchasing the required PLC, the user can simply and flexibly and conveniently apply the PLC to the production practice by simply making a small amount of wiring and simple user programming according to the instructions of the manual.
Programmable controllers have been evolving, so the final definition has not yet been made to date. The International Electrotechnical Society ( IEC ) issued the first, second and third drafts of the draft programmable controller standard in 1982.11 ; 1985.1 and 1987.2 .
In the third draft, the PLC is defined as follows: The programmable controller is a digital arithmetic operation electronic system designed for applications in industrial environments. It uses a programmable memory that stores instructions for performing operations such as logic operations, sequence control, timing, counting, and arithmetic operations, and controls various types of machinery through digital, analog inputs and outputs. Or the production process. Programmable controllers and their associated peripherals should be designed in a way that is easy to integrate with the industrial control system and easily expand its functionality.
The definition emphasizes that PLC is: 1 electronic system for digital operation - also a computer
2 Designed for industrial applications
3 user-oriented instructions - easy to program
4 logic operations, sequence control, timing calculations and arithmetic operations
5 digital or analog input and output control
6 easy to integrate with the control system
7 easy to expand
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